Polyvinyl chloride resin sheets production thereof

ABSTRACT

A polyvinyl chloride resin sheet which is excellent in resistance to scratch, wear and slip and hence suitable for use as flooring materials, which has a thickness of 50-500 μm; an embossed and matted surface of which roughness is 15-25 μm; and a transmittance of not less than 75%, and which comprises: 
     (a) polyvinyl chloride; 
     (b) a plasticizer in an amount of 5-35 parts by weight per 100 parts by weight of polyvinyl chloride; and 
     (c) short glass fibers having a diameter of 6-12 μm and an average length of 0.2-1.0 mm in an amount of 0.5-30 parts by weight per 100 parts by weight of polyvinyl chloride.

This application is a Divisional of application Ser. No. 08/616,067,filed Mar. 14, 1996, now U.S. Pat. No. 5,772,941 which application(s)are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to polyvinyl chloride resin sheets and productionthereof. More particularly, the invention relates to a substantiallytransparent and short glass fibers containing polyvinyl chloride resinsheet especially suitable for use as flooring materials on account ofits excellent resistance to scratch, wear and slip.

DESCRIPTION OF THE PRIOR ART

A variety of resin sheets containing fillers such as glass fibers arealready known and they are in wide use for a variety of purposes. Forexample, a decorative laminate is disclosed in Japanese Utility ModelPublication No. 60-33005 which has an intermediate layer of a resin inwhich short glass fibers are dispersed together with a colorant isinterposed between a translucent or opaque base layer and a transparentor translucent surface layer of a resin and which has a pattern ordesign between the intermadiate layer and the surface layer. Such adecorative laminate is elaborately designed and hence useful fordecorative purpose. However, such a decorative laminate has a surfacelayer which is not sufficient in resistance to scratch, wear or slip sothat it is not usable as flooring materials.

A protecting sheet is disclosed in Japanese Patent Application Laid-OpenNo. 56-69158 which is composed of a plasticized or semi-rigid polyvinylchloride resin sheet in which fine particles of inorganic fillers suchas silica or zeolite are dispersed and has an adhesive layer on eitheror both sides of the sheet. This sheet has improved resistance to slipto an extent, however, the sheet is also not sufficient in resistance toscratch or wear, and moreover, it is poor in transparence. A furtherdecorative laminate for interior use is also disclosed in JapanesePatent Application Laid-Open No. 6-79835 which is composed of a resinfilm in which short glass fibers are dispersed, an internallyplasticized film and an adhesive layer in this order. However, noattention is paid in connection with resistance to slip which is anessential requisite to flooring materials.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a substantially transparentpolyvinyl chloride resin sheet which contains short glass fibers and isespecially suitable for use as flooring materials on account of itsexcellent resistance to scratch, wear and slip.

It is also an object of the invention to provide a method for producingsuch a polyvinyl chloride resin sheet.

The invention provides a transparent polyvinyl chloride resin sheetwhich has a thickness of 50-500 μm; an embossed and matted surface ofsurface roughness of 15-25 μm; and a transmittance of not less than 75%,and which comprises:

(a) polyvinyl chloride;

(b) a plasticizer in an amount of 5-35 parts by weight per 100 parts byweight of polyvinyl chloride; and

(c) short glass fibers having a diameter of 6-12 μm and an averagelength of 0.2-1.0 mm in an amount of 0.5-30 parts by weight per 100parts by weight of polyvinyl chloride.

The invention further provides a method for producing a polyvinylchloride resin sheet which has a thickness of 50-500 μm; an embossed andmatted surface of which roughness is 15-25 μm; and a transmittance ofnot less than 75%, which comprises:

preparing a compound comprising

(a) polyvinyl chloride;

(b) a plasticizer in an amount of 5-35 parts by weight per 100 parts byweight of polyvinyl chloride; and

(c) short glass fibers having a diameter of 6-12 μm and an averagelength of 2-12 mm in an amount of 0.5-30 parts by weight per 100 partsby weight of polyvinyl chloride;

calendering the compound into a resin sheet with calender rolls; and insuccession, embossing the surface of the resin sheet by use of anembossing machine composed of an embossing roll and a backup roll with aratio of the peripheral velocity of the embossing roll to the peripheralvelocity of the final roll of the calender rolls being in the range of1.3-2.3.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of device arrangement of a calender machine and anembossing machine for the production of a resin sheet of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Any polyvinyl chloride which is known to be usable for calendering maybe used. Polyvinyl chloride may be used singly or it may be blended witha second resin to improve the processability or properties of polyvinylchloride. The second resin may be exemplified by, for example,ethylene-vinyl chloride copolymers, ethylene-vinyl acetate copolymers,ethylene-vinylidene chloride copolymers, vinyl chloride-(meth)acrylicester copolymers, vinyl chloride grafted polyurethane copolymers ormethyl methacrylate (copolymer) resins. The second resin may be used upto 10% by weight in the resultant blend. In particular, methylmethacrylate (copolymer) resin is useful as a modifier for polyvinylchloride.

The polyvinyl chloride or its blend as above mentioned is kneaded with aplasticizer and short glass fibers among others to prepare a uniformmixture, i.e., a compound, and the compound is then calendered toprovide polyvinyl chloride resin sheets.

The plasticizer may be any one which is known to be usable forcalendering products of polyvinyl chloride resin. For example, theplasticizer used includes, for example, phthalic acid diesters such asdiethylhexyl phthalate (DOP), linear dibasic carboxylic acid diesters,phosphoric acid esters, epoxylated soybean oil or polyesterplasticizers. Depending upon the requisites to the resultant resinsheets, the plasticizer is used usually in an amount of 5-35 parts byweight, preferably in an amount of 10-30 parts by weight, per 100 partsby weight of polyvinyl chloride used.

The short glass fibers used in the invention have a diameter of 6-12 μmand an average length of 6-12 m and are used in an amount of 0.5-30parts by weight, preferably in an amount of 1-25 parts by weight, mostpreferably in an amount of 3-20 parts by weight, per 100 parts by weightof polyvinyl chloride so that the resultant resin sheet has a surfaceroughness in the desired range after slight embossing to form a mattedsurface.

As the short glass fibers, chopped glass strands are especially usefulin the preparation of the resin sheet of the invention. The choppedglass strand is commercially available. They may be produced by sizingglass filaments with a sizing agent, preferably a silane coupling agent,gathering about 200 to 300 filaments into bundles of filaments, andcutting the bundle to a length of usually about 0.6-60 mm. In theproduction of the resin sheet of the invention, the glass strand ismixed and kneaded with polyvinyl chloride so that it is separated intoindividual short fibers and dispersed as such in the polyvinyl chloride.

When the amount of the short glass fibers used is less than 0.5 parts byweight per 100 parts by weight of polyvinyl chloride, the resultantresin sheet is still deficient in resistance to scratch, wear and slip.On the other hand, when the amount is more than 30 parts by weight per100 parts by weight of polyvinyl chloride, the resultant compound isdifficult to calender, and besides, the resultant sheet is deficient intransparence.

The compound usually contains a stabilizer, preferably metallic soapsuch as barium or zinc soap. The stabilizer is used usually in an amountof 0.5-10 parts by weight, preferably in amount of 1-5 parts by weight,per 100 parts by weight of polyvinyl chloride.

Other additives may be contained in the compound if necessary in such anamount that the incorporation thereof into the compound does notadversely affect the transparence or other desired properties of theresultant resin sheet. The additive may include, for example,lubricants, antioxidants, ultraviolet absorbers, fire retardants orantistatic agents.

The short glass fibers may be mixed and kneaded under heating togetherwith a small amount of polyvinyl chloride or plasticizer to prepare abatch, and the batch may be used in the preparation of the compound. Theuse of batch makes it easy to disperse the short glass fibers evenly inthe compound. The use of batch is also advantageous from the standpointof environmental protection since short glass fibers are not scatteredduring the preparation of the compound. By way of example, the batch iscomposed of 60-80% by weight of short glass fibers, 5-20% by weight ofpolyvinyl chloride and 10-35% by weight of plasticizer.

As well known in the art, the compound is prepared by metering andmixing the ingredients as mentioned above together, kneading andplasticizing the mixture to form a compound, feeding the compound into abank between the calender rolls, and calendering the compound to a resinsheet. The thus obtained resin sheet is then in succession supplied toan embossing machine to emboss slightly the surface of the resin sheetto form a matted sheet whereby the sheet has a desired surface roughnessin the range of 15-25 μm according to the invention.

The calender machine used in the invention is not specifically limited,however, an inverted L-type four rolls calender is preferred, asillustrated in FIG. 1. According to the invention, the resin sheet 2 istaken out of the final roll 1 of the calender rolls and the sheet isthen in succession supplied to an embossing machine 4 composed of anembossing roll 5 and a backup roll 6 via a take off roll 3 after heatingif necessary to provide polyvinyl chloride resin sheets having athickness of 50-500 μm. The embossing machine 4 is mounted to emboss theresin sheet slightly so that the resin sheet has a desired mattedsurface.

The embossing roll has a metallic surface, such as of stainless steel.It is preferred that the embossing roll has a roughness of 3-6 μm toform a matted surface of a roughness in the range of 15-25 μm,preferably in the range of 17-23 μm, most preferably in the range of17.5-21 μm, on the resin sheet by embossing the resin sheet slightlywhile applying tension to the resin sheet in the lengthwise directionaccording to the invention as set forth hereinafter. The backup roll hasusually a surface of rubber and has a roughness of 7-13 μm.

The resin sheet 2 is supplied to a gap between the embossing roll 5 andthe backup roll 6 and is embossed on the surface. It is essential thatthe resin sheet 2 is take off from the final calender roll 1 and issupplied to the embossing roll with a ratio of the peripheral velocityof the embossing roll to the peripheral velocity of the final roll ofthe calender rolls being in the range of 1.3-2.3 so that the resin sheetis stretched in the lengthwise direction thereby providing a polyvinylchloride resin sheet 8 which has a thickness of 50-500 μm, an embossedand matted surface 7 of which surface roughness is in the range of 15-25μm and a light transmittance of not less than 75%, wherein the surfaceroughness is expressed in terms of ten point average roughness (RzD). Itis most preferred that the ratio of the peripheral velocity of theembossing roll to the peripheral velocity of the final roll of thecalender is in the range of 1.5-2.1. The backup roll is driven at thesame peripheral velocity as the embossing roll.

In a preferred embodiment, the calender machine is so operated that thefinal roll 1 has a peripheral velocity of 10-25 m per minute, and theembossing machine is so operated as above mentioned so that tension isapplied to the resin sheet in the lengthwise direction, that is, theresin sheet is stretched in the lengthwise direction to reduce thethickness, thereby providing a resin sheet which contains short glassfibers having an average length of 0.2-1.0 mm in an amount of 0.5-30parts by weight, preferably 1-25 parts by weight, most preferably 3-20parts by weight, per 100 parts by weight of polyvinyl chloride, and hasa thickness of 50-500 μm, preferably 80-300 μm. As consequences, theresin sheet has an embossed and matted surface of which roughness is inthe range of 15-25 μm, preferably 17-23 μm, most preferably 17.5-21 μm,and thus has an excellent resistance to slip in terms of a coefficientof static friction as defined in ASTM D2047 of not less than 0.5.

According to the invention, in spite of the fact that an embossing rollhaving a surface roughness of 3-6 μm is used to emboss the resin sheetslightly, there is obtained a resin sheet which has an enlarged surfaceroughness in the range of 15-25 μm.

This is a first important aspect of the invention. A probable reasontherefor is that the resin sheet is taken up from the final calenderroll to the embossing roll while tension is applied to the resin sheetin the longwise direction, and accordingly while the resin sheet isstretched in the longwise direction, the resin sheet is embossed, sothat the surface of the sheet subsides at portions where no glass fibersare present to enlarge the surface roughness.

As a second important aspect, the resultant resin sheet has short glassfibers evenly dispersed therein from the surface or front to the backside so that the resin sheet is excellent in resistance to scratch andwear. Even if the resin sheet is worn at the surface to some extent, itstill retains a high resistance to slip.

As a further important aspect, the resin sheet of the invention has alight transmittance of not less than 75%, preferably not less than 80%,that is, the resin sheet is substantially transparent. Accordingly, whenit is placed on a pattern or a design, it can be seen clearly throughthe resin sheet so that it is suitable for use as decorative flooringmaterials.

The invention will be described with reference to examples, however, theinvention is not limited thereto.

EXAMPLE 1

A mixture of 200 parts by weight of chopped glass strands of short glassfibers having a diameter of 6 μm and a length of 8 mm (Glasslon ChoppedStrand 06-IE-830A available from Asahi Fiber Glass K.K.), 22.0 parts byweight of polyvinyl chloride having an average polymerization degree of700, 63.0 parts by weight of diethylhexyl phthalate and 0.7 parts byweight of epoxylated soybean oil was kneaded together under heating witha Henschel mixer to prepare a batch containing 70% by weight of shortglassfibers.

Polyvinyl chloride having an average polymerization degree of 1050,diethylhexyl phthalate, barium-zinc stabilizer, epoxylated soybean oiland a modifier were each metered and kneaded together with the glassfiber batch by use of a Henschel mixer to prepare a compound which wascomposed of 24 parts by weight of diethylhexyl phthalate, 2.5 parts byweight of barium-zinc stabilizer, 3.0 parts by weight of epoxylatedsoybean oil, 1.5 parts by weight of modifier and 3.0 parts by weight ofshort glass fibers each per 100 parts by weight of polyvinyl chloride.

The compound was supplied to a bank of an inverted L-type calender asillustrated in FIG. 1 and formed into a resin sheet having a thicknessof 200 μm with a peripheral velocity of the final calender roll of 15 mper minute and a peripheral velocity of the embossing roll of 22.5 m perminute, i,e., at a ratio of the peripheral velocity of the embossingroll to the peripheral velocity of the final calender roll of 1.5. Theemnossing roll had a surface roughness of 4.5 μm and the backup roll hada surface roughness of 10.5 μm.

The resin sheet was found to contain short glass fibers having anaverage length of 0.51 mm, and a has an embossed and matted surface ofwhich roughness was 19.5 μm and the back side of which roughness was16.1 μm. The resistance to scratch, wear and slip of the resin sheet areshown in Table 1.

The resistance to scratch was examined by a pencil scratch testaccording to JIS K 5400; the resistance to wear was examined by aTaber's abrasion resistance test with CS-17 abrasive wheels under a loadof 1 kg according to JIS K7204; the resistance to slip was examined interms of a coefficient of static friction according to ASTM D 2047. Aresin sheet having a coefficient of static friction of not less than 0.5has a resistance to slip requisite to flooring materials. Thetransmittance was measured according to JIS K 7105.

EXAMPLES 2-5

Short glass fibers were used in an amount as shown in Table 1 per 100parts by weight of polyvinyl chloride and otherwise in the same manneras in Example 1, resin sheets having a thickness of 200 μm wereprepared. The resistance to scratch, wear and slip of the sheets as wellas the transmittance are shown in Table 1.

Comparative Example 1

Except that short glass fibers were not used, a resin sheet having athickness of 200 μm was prepared in the same manner as in Example 1. Thesheet was found to have an embossed and matted surface of whichroughness was 4.0 μm and the back side of which roughness was 8.3 μm.The embossed surface and the back side was found to have substantiallythe same surface roughness as the embossing roll and the backup roll,respectively. The resistance to scratch, wear and slip of the sheets aswell as the transmittance are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________              Examples                      Comparative                                     1     2     3     4     5     1                                     __________________________________________________________________________    Content of short                                                                        3.0   5.0   10.0  20.0  30.0  0                                     glass fibers in                                                               resin sheet                                                                   (parts by weight)*)                                                           Average length of                                                                       0.51  0.60  0.58  0.61  0.55  --                                    short glass fibers                                                            in resin sheet (mm)                                                           Surface roughness of                                                                    19.5  20.0  18.5  18.5  18.0  4.0                                   embossed surface                                                              of resin sheet (μm)                                                        Resistance to scratch                                                                   H˜2H                                                                          2H    2H˜3H                                                                         2H˜3H                                                                         3H    2B                                    Resistance to wear                                                                      Good after                                                                          Good after                                                                          Good after                                                                          Good after                                                                          Good after                                                                          Worn out                                        13000 15000 13000 15000 13000 after 10000                                     revolutions                                                                         revolutions                                                                         revolutions                                                                         revolutions                                                                         revolutions                                                                         revolutions                           Resistance to slip                                                                      not less                                                                            not less                                                                            not less                                                                            not less                                                                            not less                                                                            0.2                                             than 0.5                                                                            than 0.5                                                                            than 0.5                                                                            than 0.5                                                                            than 0.5                                    Transmittance (%)                                                                       85    84    84    83    78    90                                    __________________________________________________________________________     *)Per 100 parts by weight of polyvinyl chloride                          

What is claimed is:
 1. A polyvinyl chloride resin sheet which has athickness of 50-500 μm; an embossed and matted surface of whichroughness is 15-25 μm; and a transmittance of not less than 75%, andwhich comprises:(a) polyvinyl chloride; (b) a plasticizer in an amountof 5-35 parts by weight per 100 parts by weight of polyvinyl chloride;and (c) short glass fibers having a diameter of 6-12 μm and an averagelength of 0.2-1.0 mm in an amount of 0.5-30 parts by weight per 100parts by weight of polyvinyl chloride.
 2. The resin sheet as claimed inclaim 1 which comprises short glass fibers in an amount of 1-25 parts byweight per 100 parts by weight of polyvinyl chloride.
 3. The resin sheetas claimed in claim 1 which comprises short glass fibers in an amount of3-20 parts by weight per 100 parts by weight of polyvinyl chloride andhas a transmittance of not less than 80%.
 4. The resin sheet as claimedin claim 1 which has a surface roughness of 17-23 μm.
 5. The resin sheetas claimed in claim 1 which has a surface roughness of 17.5-21 μm.